In the beverage packaging industry, beverage containers are typically manufactured in at least two parts: a container body and at least one container end. Typically, the container body is formed by drawing and ironing a sheet of metal into a cup-shaped container body. Container bodies and separate end pieces are shipped to a beverage filler. The filler provides a beverage to each container body and thereafter secures a separate container end to the open end of the body.
In forming the drawn and ironed container body from sheet metal stock, a multi-stage process is typically used. In one procedure, a circular disc is punched from a piece of sheet metal stock and provided to a drawing apparatus comprising a draw die and a draw punch. The circular disk is positioned over the upwardly open cylindrical cavity of the draw die, and is forcibly driven into the cavity by the draw punch to form a cup. The cup is then provided to a redrawing and ironing apparatus to form a container body having the desired specifications. More specifically, the cup is positioned over a redraw die and is forcibly driven therethrough by a forming punch attached to a ram. The redraw die reduces the inner and outer diameter of the cup to approximately the dimensions required for the container body. The redrawn cup is then passed through a series of ironing rings to further reduce the sidewall thickness of the redrawn cup. After passing through the last ironing ring, the end of the container body engages an outer die to form a transition wall of the container body. An inner die is subsequently advanced toward the container body to form a center panel and a nose into the bottom of the container body. The punch is subsequently retracted, and the formed container body is removed from the punch in an appropriate manner, such as by stripping (e.g., using forced air and/or fingers which engage the sidewall of the container body).
During the formation of the center panel in the bottom of the container body, material in the container body is pulled downwardly along the lower end of the sidewall and along the transition wall to provide sufficient material for formation of the center panel. This process is commonly referred to as "pulldown" of the sidewall. During pulldown of the sidewall, the material must flow from the larger diameter of the sidewall, through the transition wall, to the smaller diameter of the nose. Such change in diameter can result in wrinkling problems. Wrinkling problems have been compounded by the recent trend in reducing the diameter of the nose of container bodies, thereby resulting in a larger reduction in diameter from the sidewall to the nose.
Wrinkling can typically be remedied by increasing the force exerted by the outer die against the punch. However, such increase in force can result in excessive thinning of the wall thickness in the inner wall of the container body between the nose and the center panel. In addition, high outer die forces can increase the energy required to produce the container body, increase wear on the surfaces of the dies, and significantly reduce the life of the bodymaker mechanisms.
Accordingly, it is an object of the present invention to provide an apparatus and method for producing container bodies in a more energy-efficient, cost-effective manner. It is another object of the present invention to provide a container body configuration which can be readily produced and which facilitates energy-efficient and cost-effective production thereof. It is a related object to provide such a container body which allows for a reduction in the outer die forces required to produce a satisfactory container body.